For most of us, genetic inheritance plays a limited role in
determining our health. More important is where and how we live,
work, and play -- the quality of what we drink, eat, and breathe.
From the time of conception, throughout development, and into
early and late adulthood, environmental factors either directly
impact biological tissues or influence gene expression and shape
subsequent disease risks.

Although links between exposures to environmental contaminants
and health impacts have been known for centuries, recent research
documents an expanding list of previously unrecognized effects
after fetal or infant exposures.[1] The developing fetus and
child are particularly vulnerable to toxic insults. During this
time cells are rapidly dividing, and growth is dramatic. Various
events, including development of the brain and endocrine,
reproductive, and immune systems, are uniquely susceptible to
disruption that is often permanent. To compound the problem,
pound for pound, children are often disproportionately exposed to
toxic environmental agents because of the way they breathe, eat,
drink, and play. Moreover, immature detoxification pathways in
children frequently result in increased impacts of toxic
exposures when compared to adults.

Small exposures to substances like lead, mercury, or
polychlorinated biphenyls (PCBs), which have no discernible
impact on adults, can permanently damage the developing brain of
a child, if the exposure occurs during a window of vulnerability.
Early exposures to dioxin or polychlorinated biphenyls (PCBs),
chemicals from industrial activities that bioaccumulate in
dietary fat, damage the developing immune system, making the
child more prone to infections.[2] Risks of asthma and high blood
pressure are increased by early environmental exposures.[3,4]
Recent research from Sweden concludes not only that environmental
factors play a more important role than genetic inheritance in
the origin of most cancers, but also that cancer risk is largely
established during the first 20 years of life.[5,6]

Technological developments have dramatically reduced mortality
resulting from many diseases. In many instances, however, disease
incidence is increasing, although for some conditions without
standardized tracking mechanisms, trends are difficult to
determine accurately. The burden from current patterns of disease
and disability is enormous and extracts a terrible toll from
individuals, families, and communities. Nearly 12 million
children in the U.S (17 percent) suffer from one or more
developmental disabilities, including deafness, blindness,
epilepsy, speech defects, cerebral palsy, delays in growth and
development, behavioral problems, or learning disabilities.[7]
Learning disabilities alone affect 5 to 10 percent of children in
public schools, and these numbers appear to be increasing.

Attention deficit hyperactivity disorder conservatively affects 3
to 6 percent of all school children, and the numbers may be
considerably higher. The incidence of autism seems to be
increasing, though much of this apparent increase may be due to
increased reporting. The age-adjusted incidence of melanoma, lung
(female), prostate, liver, non-Hodgkin's lymphoma, testis,
thyroid, kidney, breast, brain, esophagus, and bladder cancers
has steadily increased over the past 25 years.[8] Some birth
defects, including disorders of the male reproductive system and
some forms of congenital heart disease, are increasingly
common.[9,10] Sperm counts and fertility are in decline in some
areas of the U.S. and other parts of the world.[11] Asthma is
more common and more severe than ever before.[12] Genetic factors
explain far less than half of the population variance for most of
these conditions. Although smoking and sun exposure are
well-recognized risk factors for some conditions, improved
understanding of development of the brain and the immune,
reproductive, respiratory, and cardiovascular systems leads to
the conclusion that other environmental factors play a major role
in determining current patterns of disease.

To the limited degree that health care providers address
environmental factors at all, most focus nearly all of their
attention on personal behaviors, like smoking, substance abuse,
or use of sunscreens. These are more easily addressed by
individuals than more complex problems like air and water
pollution, hazardous waste sites, agricultural systems that
inevitably result in farmworker pesticide exposures, and mercury
contamination of dietary fish. Global environmental conditions,
however, are changing, along with the changing pattern of disease
and disability, and our increasing understanding of the
importance of environmental factors in determining the health of
individuals and populations places a new and special
responsibility on the medical profession.

Consider that:[13,14]

** Over 6 billion people inhabit the planet, and reasonable
mid-level estimates predict 9 to 10 billion by mid-century.
Two-and-a-half more "earths" would be needed to support today's
population if everyone were to use as many resources as Americans
do on a per capita basis.

** The release of ozone-depleting chemicals used for industrial
and agricultural purposes has depleted the stratospheric ozone
layer and is likely a major contributor to the increased
incidence of malignant melanoma.

** Carbon dioxide concentration in the atmosphere has increased
by nearly 30 percent in the last 150 years. Carbon dioxide is a
greenhouse gas that contributes to global warming. Hazardous air
pollution, in general, is the norm in most parts of the U.S. and
elsewhere in the world.

** Humans are responsible for more atmospheric nitrogen fixation
than all other sources combined. Nitrates contaminate
groundwater, surface water, and air at toxic concentrations.

** Humans are responsible for most of the mercury deposition on
the surface of the earth. Mercury makes its way into the food
chain, where it bioconcentrates. In most states, freshwater and
marine fish are sufficiently contaminated with mercury to require
warnings to women of reproductive age to limit consumption
because of risks to fetal brain development.

** Large numbers of plant and animal species have been driven to
extinction, and most marine fisheries are severely depleted. More
than half the world's coral reefs are threatened by human
activities.

** In addition to naturally occurring products like lead and
mercury that are mined from the earth, novel synthetic industrial
chemicals contaminate the world's ecosystems, its human and
non-human inhabitants, their breast milk and egg yolk, ovarian
follicles, amniotic fluid, and meconium. The toxicity of most is
little known.

** Of the approximately 85,000 chemicals on the federal
inventory, nearly 3,000 are produced in excess of 1 million
pounds annually. For these high-production volume (HPV)
chemicals, toxicity data are surprisingly sparse. Even basic
toxicity testing results are not publicly available for 75
percent of them.[15] In the U.S., according to the 2000 Toxics
Release Inventory, over 6.2 billion pounds of the listed toxic
chemicals, including 2 billion pounds of known or suspected
neurotoxicants, were released into the environment by major
emitters required by federal law to file reports. Emissions from
small industries and neighborhood shops are unquantified. The
extent of exposure from these releases and from the use of
various consumer products that contain them is also largely
unknown, but population-based surveys give an indication of the
ubiquity of exposures.[16]

As the industrial revolution has continued to unfold over the
last century, humans have fundamentally altered the local and
global environment. We see signals and changing patterns in the
development of children and subsequent occurrence and
distribution of disease that deserve serious attention. The
medical community is challenged to widen its scope of
responsibility to embrace a more ecological assessment and
response to the emerging pattern of disease and disability.

Early in their training, health care providers are taught to
inquire into the family and social history of their patients or
clients. This is not enough. Specific knowledge of the home,
community, workplace, and school environment is essential for
identifying risks and mapping preventive strategies. Medical
education needs to incorporate into the curriculum new
understanding of the role of the environment in the development
of disease and disability. Health clinicians can also play
important roles in policy debates at the community, state, or
national level. The division between medical practice and public
health practice that began in the early 20th century has not
narrowed nearly enough. Health care providers can become strong
advocates for clear air and water, for communities free of
hazardous waste sites, and schools free of toxic chemicals and
mold.

The public supports a large medical-industrial complex, but that
support is not limitless. It is time for the medical community to
re-examine its priorities and social contract with the public,
and to integrate fully and creatively into routine medical care
what we know about the causes of the changing pattern of diseases
and disabilities.[17]

==========

* Dr. Schettler is on the medical staff of Boston Medical Center
and has a clinical practice at the East Boston Neighborhood
Health Center. He is science director of the Science and
Environmental Health Network (http://www.sehn.org). Dr.
Schettler is co-author of GENERATIONS AT RISK: REPRODUCTIVE
HEALTH AND THE ENVIRONMENT, which examines reproductive and
developmental health effects of exposure to a variety of
environmental toxicants. He is also co-author of IN HARM'S WAY:
TOXIC THREATS TO CHILD DEVELOPMENT, which discusses the impact
of environmental exposures on neurological development in
children. (See Rachel's #712.)